configure: Disable XCB auto-detection on Mac

Users might have (old) libxcb installed on OS X, for instance as
a dependency for another package installed via MacPorts. It's still
very unlikely that any Mac user would want to use the XCB platform
plugin. Thus, disable the auto-detection to avoid a dubious XCB
configuration error on Mac.

Change-Id: I11d21aad255925883d6841444baa13a29f1a26b0
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Gatis Paeglis <gatis.paeglis@digia.com>
Apply fontconfig settings to custom fonts

Currently QtWebKits custom fonts does not follow the system settings
on Linux. This is because they are only handled by the basic
fontdatabase.

This patch adds handling of custom fonts to QFontconfigDatabase.

Change-Id: I676fc97840766b58cd937bb8e2c9f166f30c8a6e
Reviewed-by: Pierre Rossi <pierre.rossi@gmail.com>